JP5861751B2 - Method for producing biaxially stretched polyamide resin film - Google Patents

Description

  The present invention generally relates to a film made of a resin containing a layered compound called a nanocomposite. More specifically, the present invention relates to a stretched film of a nanocomposite polyamide resin, which has been said to be impossible to stretch at a high magnification with an addition amount of 1% or more.

  Since the slipperiness of conventional nylon films changes with humidity, when slipperiness under high humidity is required, the surface roughness is roughened to make it slippery, but inorganic layered compounds are used. In conventional films, the change in slipperiness due to humidity is small, and even if the surface roughness is small, sufficient slipperiness is exhibited, so that conflicting properties such as gloss can be achieved.

  Biaxially stretched polyamide resin films are excellent in mechanical properties, barrier properties, pinhole resistance, transparency and the like, and are widely used as packaging materials. However, due to the high hygroscopic property derived from the amide bond in the resin skeleton, the mechanical strength changes due to the change in humidity, and hygroscopic elongation occurs, and problems are likely to occur in various processes. In addition, the glass transition point of the resin itself is not so high, and it is desired to improve heat resistance, particularly mechanical properties at high temperatures.

  As a method for improving heat resistance and hygroscopicity of polyamide resin, it is known to uniformly disperse layered silicate, and this method is known as nanocomposite formation. Since various properties described above are improved by nanocompositing, it is expected that a film with improved properties will be obtained by filming, but in reality, these resins are generally poor in stretchability, It is not suitable as a resin for stretched films. In particular, it is said that it is necessary to add 1% or more of a layered silicate to a polyamide resin in order to sufficiently enhance the effect of improving the mechanical properties, but a polyamide resin having such a high layered silicate content. Then, the difficulty of stretching was remarkable.

  Patent Document 1 discloses a biaxially stretched polyamide film containing a layered silicate, but in order to overcome the difficulty of stretching, the maximum temperature reached 180 ° by successive stretching in the width direction next to the length direction. A high temperature of −200 ° C. is essential, and the layered silicate is not sufficiently oriented because the crystal proceeds excessively before sufficient stretching in the width direction is achieved, as well as difficulty in production. In other words, there are problems that the effect of adding various layered silicates does not appear, thickness spots occur in fine regions, and pinhole resistance is not achieved.

  Furthermore, even if such a special method is adopted, as can be seen from the claims, it is practically 1% by weight or less (including the organic component contained between the layers), and beyond that, whitening during stretching, It has been pointed out that the productivity is poor at high stretch ratios. This is considered to be because stress tends to concentrate on the tip of the layered compound during stretching, and glazes and cracks are likely to occur.

  Patent Document 2 also discloses a patent for a stretched film in which a layered inorganic compound is added in an amount of 0.5 to 5%, but there is no specific measure for solving the above-described poor stretchability. There is no description, and it is the result of examination at the level where small pieces were simultaneously biaxially stretched in the laboratory, industrial production by sequential biaxial stretching in a system to which a layered compound at a high concentration of 1% or more was added There is no technical disclosure about the stretching method having the property. In addition, there is a description in the text that layered inorganic compounds such as montmorillonite are effective in improving slipperiness by blocking water absorption, but when a material such as montmorillonite is added to nylon resin, the equilibrium water absorption rate of the resin is To increase. From this, it can be said that the essence of the invention largely depends on the effect of addition of the inorganic lubricant.

  As described above, industrial production of a stretched film made of a polyamide resin excellent in the above-described various properties has been difficult on the extension lines of the prior art.

  In general, in order to give the film slipperiness, particles are added as a lubricant to form protrusions on the surface. However, in the case of a polyamide film, the resin becomes soft and slipperiness decreases due to an increase in humidity. In order to achieve the slipperiness at the same time, it was necessary to make the surface rough and to be slippery. Therefore, the polyamide film with improved slipperiness under high humidity has problems such as poor gloss.

JP 2003-20349 A JP 2003-313322 A

  In the present invention, a polyamide resin in which a layered compound represented by a layered silicate that has been conventionally difficult to stretch is uniformly dispersed is stretched under the same stretching conditions as a conventional polyamide resin not containing a layered compound. It is an object of the present invention to provide a polyamide resin film excellent in hygroscopic dimensional stability, high humidity and high temperature, high slip properties, and handling properties.

  The present inventors consider that a problem in stretching is that cracks are easily generated along the layered compound due to stress in a direction perpendicular to the plane of the layered compound, and the orientation state of the layered compound and reduction of the stretching stress As a result of investigation, in the conventional method, since the molecular chain is fixed by the layered compound, when the cast sheet is stretched vertically, a large stress is applied to the molecular chain in the width and thickness directions. Considering that it was difficult to stretch, the shear stress was applied evenly to the sheet at the time of casting to promote the orientation of the layered compound in the in-plane direction, and the generation of crazes and cracks caused by the stress concentrated on the tip of the layered compound And a method that can reduce the entanglement density in the thickness direction at the same time. . Furthermore, the film obtained by adopting such a method has been found that the layered compound is oriented at a high level and has excellent characteristics not found in the past, and has led to the present invention.

That is, this invention consists of the following structures.
1. An inorganic substance containing a layered compound is added in an amount of 0.3 to 10% by weight, and the polyamide resin used in the biaxially stretched polyamide resin film is a kind of resin selected from nylon 6, nylon 66, and metaxylylenediamine-based nylon. The compound is oriented in-plane, the haze is 1.0-20%, the elastic modulus in the longitudinal direction at a relative humidity of 35% RH is 1.7-3.5 GPa, the surface roughness (Sa) is 0.01-0.1 μm, the normal stress When the coefficient of static friction (F / B) at 0.5 N / cm ² is 0.3 to 1.0 and the refractive index of the central portion in the width direction of the film is Ny, Ny (A) which is Ny of the sheet before longitudinal stretching A method for producing a biaxially stretched polyamide resin film in which the difference Ny (A) −Ny (B) from Ny (B) of the sheet after longitudinal stretching is 0.001 or more, and a speed of 2000% / min or less The manufacturing method of the biaxially stretched polyamide resin film characterized by including the process stretched | stretched longitudinally.
2. 2. The method for producing a biaxially stretched polyamide resin film as described in the first item, wherein the number of pinholes after 1000 gelboflex tests at 23 ° C. is 0-30.
3. 3. The method for producing a biaxially stretched polyamide resin film according to the first or second aspect, wherein the biaxially stretched polyamide resin film is stretched at a transverse stretching temperature of 50 to 155 ° C.
4 . The method for producing a biaxially stretched polyamide resin film as described in any one of 1 to 3 above, wherein the stretching in the longitudinal direction is a single step or a two-step stretch.

  According to the present invention, a polyamide resin in which a layered compound is uniformly dispersed, which has been difficult to obtain a good strength and appearance in the conventional stretching method, is stretched uniformly and without deterioration in appearance. By this method, it is possible to provide a polyamide resin film excellent in slipperiness under high humidity and generally excellent in surface gloss which is difficult to achieve at the same time.

The present invention is described in detail below.
(Polyamide resin)
The polyamide resin used in the present invention is not particularly limited, such as a ring-opening polymer of a cyclic lactam, a condensate of diamine and dicarboxylic acid, and a self-condensate of amino acids. For example, nylon 6, nylon 7, nylon 66, Examples include, but are not limited to, nylon 11, nylon 12, nylon 4, nylon 46, nylon 69, nylon 612, and metaxylylenediamine-based nylon. It is also possible to use a copolymerized polyamide resin. Specifically, nylon 6 and nylon 66 copolymerized with metaxylylenediamine, nylon 6T, nylon 6I, nylon 6 / 6T copolymer, nylon 6 / 6I copolymer, nylon 6 / polyalkylene glycol resin, nylon 11 / Polyalkylene glycol resin, nylon 12 / polyalkylene glycol resin, nylon 6 / MXD6 copolymer and other aromatic polyamide resins can be used, but other components copolymerized can also be used, preferably nylon 6, nylon 66, and metaxylylenediamine-based nylon are preferable. In particular, gas permeability can be greatly reduced by laminating a small amount of a layer made of metaxylylenediamine-based nylon resin, which is one of the preferred examples in the present invention.

  In addition to the polyamide resin described later, other resins and additives may be added to these resins. Moreover, it is one of preferable embodiments that the collection film manufactured by this patent is used as a part or all of the polyamide resin from the economical aspect. As other resins, known resins such as polyester resins, polyurethane resins, acrylic resins, polycarbonate resins, polyolefin resins, polyester elastomer resins, polyamide elastomer resins can be used, but are not limited thereto.

(Layered compound)
Examples of the layered compound include layered compounds such as swellable mica, clay, montmorillonite, smectite, and hydrotalcite, but are not limited to these and can be used regardless of inorganic or organic. The shape of the layered compound is not particularly limited, but the average length of the major axis is 0.01 to 50 μm, preferably 0.03 to 20 μm, particularly preferably 0.05 to 12 μm, and the aspect ratio is 5 to 5000. Preferably, those having 10 to 5000 can be suitably used.

  The addition amount of the inorganic substance containing the layered compound with respect to the polyamide resin is preferably 0.3 to 10% by weight. The inorganic layered compound may be added as an organically treated layered compound, and the amount added may not always match the content of inorganic substances (added amount) due to the weight residue described below. In addition, if a method for obtaining from a weight residue as described later is employed, a small amount of an inorganic substance other than the layered inorganic compound may be added in addition, and in the present invention, it is obtained as an added amount of the inorganic substance containing the layered compound. become. The content of the inorganic substance containing the layered compound in the present invention is a value obtained by subtracting ash from the weight residue obtained by a calorimeter (TGA). Specifically, the temperature rises from room temperature to 550 ° C. of the resin containing the layered compound. Obtained weight residue after warming, and then obtained by subtracting the value of resin ash. In the case of Example 1, the inorganic content was 2.6% by subtracting 4.4% weight residue by TGA and 1.8% weight residue from resin. Can be sought. Further, the ratio of the organic treating agent in the layered compound can be obtained separately by TGA and calculated from the numerical value. The lower limit value of the amount of the inorganic substance containing the layered compound is more preferably 0.3%, further preferably 0.7%, and particularly preferably 1.0%. If it is less than 0.3%, it is small in terms of dimensional stability and mechanical properties, and therefore the effect of adding a layered compound is small and not preferable. In addition, the coefficient of static friction increases and slipperiness may decrease. The upper limit is more preferably 10% or less, and still more preferably 8% or less. If it exceeds 10%, the effects in terms of dimensional stability and mechanical properties are saturated, which is not economical, and the fluidity at the time of melting is also lowered. In addition, the surface roughness becomes unnecessarily large or haze decreases.

  Although these layered compounds can be used in general, commercially available organically treated products that are suitably used in the monomer insertion polymerization method described below include Cloisite from Southern Clay Products, Somasif and Lucentite from Corp Chemical, Examples include Hosoon Sben.

In the present invention, it is preferable that the layered compound is uniformly dispersed in the above-described polyamide resin.
1. Intercalation method:
1) Monomer insertion polymerization method 2) Polymer insertion method 3) Organic low molecular insertion (organic swelling) kneading method In-situ method: In-situ filler formation method (sol-gel method)
3. The ultrafine particle direct dispersion method can be used. Examples of commercially available materials include Cress AlonNF3040 and NF3020 manufactured by Nanopolymer Composite Corp., NCH 1015C2 manufactured by Ube Industries, Imperm103 and Imperm105 manufactured by Nanocor, and the like. The layered compound is preferably treated with various organic treating agents for the purpose of enhancing the dispersibility of the layered compound in order to suppress the generation of coarse compounds of the layered compound contained in the polyamide resin. In order to avoid adverse effects due to thermal decomposition of the treatment agent, those obtained by using a low molecular weight compound having good thermal stability or a monomer insertion polymerization method without using a low molecular weight compound are preferred. Regarding thermal stability, a compound having a 5% weight loss temperature of 150 ° C. or higher of the treated layered compound is preferable. TGA etc. can be used for the measurement. A film having low thermal stability is not preferable because bubbles are generated in the film or coloring is caused. (See “Challenging Nanotech Materials: Polymer Nanocomposites with Expanding Applications”, Sumitomo and Tsutsunaka Techno Co., Ltd.)

These layered compounds are preferably oriented in the plane of the obtained film in order to develop the characteristics. The in-plane orientation can be confirmed by observing the cross section using a transmission electron microscope or a scanning electron microscope.

(Film forming method)
In the stretching of the resin containing a layered inorganic compound in the present invention, the problems in stretching using sequential biaxial stretching in the order of length-width which is generally advantageous in terms of economy are as follows: In stretching in the direction (hereinafter abbreviated as MD), crystallization proceeds due to heat during stretching, and the stretchability in the transverse direction (hereinafter abbreviated as TD) is lost after uniaxial stretching. (2) Breakage occurs during TD stretching There are three points: (3) Fracture occurs when heat-set after TD stretching. Regarding (1), MD stretching conditions that allow TD stretching and MD stretching conditions that do not allow TD stretching are arranged. It was found that there was a difference in the refractive index in the width direction of the uniaxially stretched sheet after MD stretching (refractive index in the Y-axis direction, hereinafter abbreviated as Ny). Specifically, Ny of a uniaxially stretched sheet capable of TD stretching is smaller than Ny after MD stretching, whereas TD stretching cannot be performed (that is, whitening or breaking occurs during TD stretching). Ny showed little or no change in Ny after MD stretching. In normal polyamide resin stretching, Ny after MD stretching causes necking in the width direction during MD stretching and Ny decreases at the same time, but when layered compounds are added, necking occurs but the layered It was found that Ny tends not to decrease due to the interaction between the compound and the polyamide resin molecule. This is because the molecular chains of the film before stretching are randomly oriented in the MD and TD directions, so when the molecular chains are stretched in the MD direction by MD stretching, force in the TD direction is also generated, but normal polyamide In the stretching of the resin, the force applied in the TD direction can be released by necking in the TD direction. On the other hand, in the case of the polyamide resin containing the layered compound, the molecular chain is constrained by the layered compound. Because the force in the direction cannot be released and the molecular chain is stretched in the TD direction as well, or the layered compound rotates during MD stretching. It was thought that the molecule was pulled in the direction of. That is, the surface orientation is already high after MD stretching. For this reason, it was thought that the stretching stress at the time of subsequent TD stretching increased, and the fracture occurred.

  As a method for solving this, by adopting a stretching condition in which Ny is reduced after MD stretching, it is possible to stretch at a high magnification without causing rupture or the like in subsequent TD stretching, and the biaxially stretched polyamide resin of the present invention It has become possible to produce films on an industrial scale.

  Ny (A) -Ny (B) is preferably 0.001 or more when the refractive index in the width direction before longitudinal stretching is Ny (A) and the refractive index in the width direction after longitudinal stretching is Ny (B). . Further, it is preferably 0.002 or more, most preferably 0.003 or more.

  As a method of lowering Ny after uniaxial stretching, a method of greatly reducing the MD stretching speed can be applied, but the same effect can be obtained by multilayering the unstretched sheet after melt extrusion. Ny can be reduced by reducing the molecular chain entanglement density in the thickness direction by multilayering, thereby improving the ease of deformation of the molecular chain, and as a result, the plane orientation during MD stretching Can be suppressed and TD stretchability can be improved. It has been found that these methods can improve the biaxial stretchability, and can realize a stretched film that is industrially highly practical and excellent in properties.

(Structure of the film)
The biaxially stretched polyamide resin film of the present invention is essentially obtained by stretching an unstretched polyamide resin sheet having a polyamide resin layer in which a layered compound is uniformly dispersed. However, it is more preferable to stretch a multilayered sheet from an industrial aspect.

  The case of multilayering is described below.

  Regarding the total number of layers and the thickness of the layers, the lower limit of the number of layers is more preferably 6 layers or more, and still more preferably 8 layers or more. If it is less than 6 layers, the in-plane orientation of the layered compound in the state before stretching is low, and the effect for reducing the stretching stress is small.

  The upper limit of the number of layers is preferably 10000 layers or less, and more preferably 5000 layers or less. Exceeding 10,000 layers is not preferable because the effect of improving stretchability is saturated and a decrease in heat shrinkage is observed.

  Further, the lower limit of the layer thickness is more preferably 10 nm, and even more preferably 100 nm, in the state before stretching. If it is less than 10 nm, the crystal size in the layer becomes too small and the thermal shrinkage rate becomes large, which is not preferable.

  The upper limit of the layer thickness is preferably 30 μm, and more preferably 20 μm. If it exceeds 30 μm, the in-plane orientation of the layered compound in the state before stretching is low, and the effect for reducing the stretching stress is small, which is not preferable.

(Lamination method)
In the present invention, when the above-described polyamide resin is multilayered, it is possible to laminate the same kind of resin in addition to the lamination of different kinds of commonly employed resins. Here, it may be difficult at first glance to find out the physical meaning of multilayering the same kind of resin by the method described later, but in an actual system, the same kind of resin was melt-extruded and laminated at the same temperature. In some cases, the interface of the layers does not disappear and exists even after stretching. This is synonymous with the fact that it is very difficult to eliminate the weld line of the injection molded product. Thus, even if it is the same kind of resin, a multilayer state is maintained, and it is possible to maintain low molecular entanglement in the thickness direction. As a method of confirming the existence of the interface of the layers when melt-extrusion and lamination of the same kind of resin, after cooling the sample with ice or liquid nitrogen, cutting out with a razor or the like, creating a cross section, and then immersing it in a solvent such as acetone It can be observed by a method of observing the cross section with a microscope.

  Polyamide resin and, if necessary, the resin composition constituting the other layers are supplied to separate extruders and extruded at a temperature equal to or higher than the melting temperature, but the melting temperature is 5 ° C. lower than the decomposition start temperature or lower. It is preferable that Also, in order to suppress cracking of the layered compound in the resin, the melting conditions and the melting temperature should be set carefully. For example, in the case of a high molecular weight polyamide resin, the melting point is less than + 10 ° C., for example. When melting at a low temperature, the layered compound is cracked, the aspect ratio is smaller than the initial state, and the effect of using the layered compound with a high aspect ratio is reduced, so there is no problem in terms of thermal stability It is preferable to melt at a high temperature.

  The polyamide resin and, if necessary, the resin composition constituting the other layer are laminated by various methods, and methods such as a feed block method and a multi-manifold method can be used. In the case of the feed block method, when the width is expanded to the die width after lamination, if there is a large difference in melt viscosity between the layers to be laminated or a temperature difference during lamination, lamination unevenness will occur, resulting in deterioration in appearance and thickness unevenness. Therefore, care should be taken during manufacturing. In order to suppress unevenness, etc., the melt viscosity at the time of extrusion is adjusted by (1) lowering the temperature, (2) adding various additives such as polyfunctional epoxy compounds, isocyanate compounds, carbodiimide compounds, etc. Preferably it is done.

  In the present invention, the in-plane orientation of the layered compound is promoted by the shearing force at the time of lamination, whereas the stress concentration at the time of stretching is concentrated at the tip of the layered compound, making it difficult to break. As a suitable method for such purpose, lamination by a feed block method or a static mixer method is preferable.

  The difference in melting temperature of each layer when the polyamide resin is laminated is 70 ° C. or less, preferably 50 ° C. or less, more preferably 30 ° C. or less. In addition, the difference in melt viscosity of the resin between the layers is within 30 times, preferably within 20 times, more preferably within 10 times the estimated shear rate in the die, thereby suppressing the appearance and unevenness during lamination. It becomes possible. In adjusting the melt viscosity, the addition of the aforementioned polyfunctional compound can be used. The static mixer temperature or feed block temperature at the time of lamination is 150 to 330 ° C, preferably 170 to 220 ° C, more preferably 180 to 300 ° C. A higher viscosity during laminating results in a better laminating state, so a lower feedblock temperature or static mixer temperature is preferable, but if the feedblock temperature or static mixer temperature is too low, the melt viscosity becomes too high and the extruder is fed. This is not preferable because the load on the surface becomes too large. When the temperature is high, the viscosity is too low and uneven lamination occurs, which is not preferable.

  Multi-manifold stacking is also possible, and the above-mentioned problem of uneven stacking is unlikely to occur. However, when laminating layers with different melt viscosities, poor wraparound of each layer resin occurs at the end. In this case, it is preferable to control the difference in melt viscosity.

  The die temperature is the same as described above, but is preferably in the range of 150 to 300 ° C, preferably 170 to 290 ° C, more preferably 180 to 285 ° C. If the temperature is too low, the melt viscosity becomes too high and the surface becomes rough and the appearance deteriorates. An excessively high temperature is not preferable because, besides the thermal decomposition of the resin, the difference in melt viscosity becomes large and unevenness occurs as described above, and particularly unevenness with a small pitch occurs.

  About the thickness of each layer before extending | stretching, it is preferable to make each layer into the range of 0.01-30 micrometers. When the thickness of the resin layer exceeds 30 μm, the effect of improving stretchability is low, which is not preferable for the present invention. If it is less than 0.01 μm, the heat shrinkage rate after heat setting becomes large, and it becomes difficult to balance with various properties, which is not preferable.

(Stretching method)
The biaxially stretched polyamide resin film of the present invention can be stretched by sequential biaxial stretching and simultaneous biaxial stretching of an unstretched sheet melt-extruded from a T die, and a method such as a tubular method can be used, but sufficient orientation In order to perform this, a method using a biaxial stretching machine is preferable. A preferable method from the standpoints of characteristics and economy includes a method of stretching in the longitudinal direction with a roll type stretching machine and then stretching in the transverse direction with a tenter type stretching machine (sequential biaxial stretching method). As for MD stretching, as described above, it has been stated that it is preferable to reduce Ny during MD stretching in order to improve TD stretchability, but in order to reduce Ny while increasing the MD stretching ratio. It is preferred to use MD multi-stage stretching.

  A substantially unoriented polyamide resin sheet obtained by melt extrusion from a T-die is stretched 2.5 to 10 times in the longitudinal direction at a glass transition temperature Tg ° C. or higher and 150 ° C. or lower of the polyamide resin, and further obtained. A longitudinally stretched film is stretched 3.0 to 10 times at a temperature of 50 ° C. or higher and 155 ° C. or lower of a polyamide resin, and then the biaxially stretched polyamide resin film is heat-set at a temperature range of 150 to 250 ° C. Is preferred.

  The temperature rising crystallization temperature can be determined by heating the sample that has been rapidly cooled after melting the resin by DSC.

  In MD stretching, when the temperature of the film is lower than the glass transition temperature (Tg) of polyamide, problems such as breakage and thickness unevenness due to orientation crystallization due to stretching occur. On the other hand, when the temperature of the film exceeds 150 ° C., breakage occurs due to crystallization by heat, which is inappropriate. Further, if the draw ratio in MD stretching is less than 1.1 times, problems such as poor quality such as thickness unevenness and insufficient strength in the longitudinal direction occur, and if it exceeds 10 times, subsequent TD stretching becomes difficult. A preferable draw ratio is 3.0 to 5.0 times.

  Furthermore, when the temperature of the film in TD stretching is a low temperature of less than 50 ° C., the TD stretchability is poor and breakage occurs, and the thickness variation in the TD direction due to neck stretching increases, which is not preferable. When the temperature is higher than (Tm) −20 ° C., thick spots increase, which is not preferable. In addition, when the TD stretch ratio is less than 1.1 times, unevenness in the thickness of the TD direction increases, which is not preferable, and the strength in the TD direction is reduced. Is also not preferable, and the draw ratio is preferably 3 times or more. Further, when the TD stretch ratio is higher than 10 times, it is substantially difficult to stretch. A particularly preferable TD stretch ratio is 3.0 to 5.0 times.

  The stretching temperature is sufficient to exhibit the effect of adding the layered silicate, and stretching at a low temperature is preferred in terms of film thickness unevenness, gelboflex resistance and the like. Preferable conditions include stretching so that the film temperature is 155 ° C. or lower during stretching.

  Further, as a preferable production method in the present invention, both ends in the width direction of the unstretched sheet multi-layered by the static mixer method or the feed block method are cut off by using a method such as cutting as necessary, and the final pre-stretching method is performed. For example, after the thickness of each layer laminated at the end is at least 30 μm, the film is stretched in at least one direction. In the above multi-layering method, depending on the structure of the die, the number of end layers may be reduced due to imperfect division of layers during layering or disorder of the layers. The layer thickness of the polyamide resin in which the layered compound having poor stretchability is dispersed may be large. For this reason, the layer thickness becomes larger than 30 μm, the stretchability of the end portion is greatly reduced, and phenomena such as whitening and breakage of the end portion may be observed during stretching. In the present invention, in this case, for the purpose of correcting the layer thickness of the end portion to the desired thickness at the time of manufacture, trimming the end portion of the unstretched sheet and then stretching is one of preferred manufacturing methods. It is.

(Heat fixing)
When the heat setting temperature is lower than 150 ° C., the effect of improving the dimensional stability due to the heat of the film is small and inappropriate. On the other hand, a high temperature exceeding 250 ° C. is inappropriate because it causes poor appearance due to whitening caused by thermal crystallization of polyamide and a decrease in mechanical strength.

  In heat setting after TD stretching, density increase due to crystallization and accompanying volume shrinkage occur. However, in the case of a resin containing a layered compound, the generated stress is very large. May break. For this reason, as a heating method at the time of heat setting, it is preferable to increase the amount of heat in a stepwise manner to suppress the generation of a rapid contraction stress. As a specific method, there are methods such as gradually increasing the temperature or increasing the air volume from the vicinity of the entrance of the heat setting zone to the vicinity of the exit, and gradually reducing the air volume in terms of the heat shrinkage rate after stretching and heat setting. The heat setting method which raises is preferable.

  Regarding the relaxation treatment, it is preferable to determine the relaxation rate in consideration of the balance with the thermal contraction rate in the vertical direction. In the present invention, since the longitudinal dimension change in moisture absorption is small, the relaxation rate is preferably in the range of 0 to 5%. If it exceeds 5%, the effect for reducing the thermal shrinkage in the width direction is small, which is not preferable.

Next, a method for greatly reducing the MD stretching speed mentioned as another method will be described.
As a method for significantly reducing the MD stretching speed, it is preferable to set the MD stretching speed to 2000% / min or less. Furthermore, it is preferable that it is 1000% / min or less. In such low-speed MD stretching, it is possible to stretch while unraveling the molecular chain constrained by the layered compound. Therefore, it is presumed that Ny decreases after MD stretching. In addition, the above-described conditions can be adopted as the MD stretching temperature, TD stretching conditions, and heat setting conditions.

  Industrially, the film thus obtained is used for various applications as it is or in the form of a roll film wound around a paper tube or the like after undergoing processing such as printing or laminating. The roll film is preferably 30 cm or more in width. The length is preferably 500 m or more. The upper limit of the width is usually about 600 cm, and the upper limit of the length is about 20000 m. A wide film or a long film immediately after film formation is slit according to the application, and is usually used as a roll film having a width of 200 cm or less and a length of 8000 m or less.

(Plane orientation)
The polyamide resin film in the present invention has a plane orientation (ΔP) after biaxial stretching, heat setting, and relaxation treatment of 0.03 or more, preferably 0.05 or more. The plane orientation is obtained by the following formula, where birefringence is obtained from a refractometer, the refractive index in the longitudinal direction is Nx, the refractive index in the width direction is Ny, and the refractive index in the thickness direction is Nz.
ΔP = (Nx + Ny) / 2-Nz

  The increase in the plane orientation can be increased by increasing the biaxial stretching ratio, particularly the TD stretching ratio. If the plane orientation is 0.03 or less, the mechanical strength such as puncture strength is lowered, which is not preferable. On the other hand, if it exceeds 0.07, productivity is lowered, which is not preferable.

(Film characteristics-haze)
The haze of the biaxially stretched polyamide resin film in the present invention is preferably in the range of 1.0 to 20%. If the haze at the time of stretching is 1.0% or less, it is difficult to produce stably, which is not preferable. If the haze exceeds 20%, it is not preferable because the design properties are deteriorated in addition to making it difficult to see the contents during use.

  The haze in the present invention is the sum derived from the resin, the layered inorganic compound, and the void derived from the peeling of the resin during stretching on the surface of the layered inorganic compound, but it is particularly preferable to reduce the haze derived from the void. The conditions are preferably set carefully. Specifically, when the MD temperature is too low, the haze increases due to the formation of voids, which is not preferable. Also, when the TD temperature is too high, haze increases due to crystallization, which is not preferable. The preferred temperature range is as described above, but can be adjusted with reference to this. Furthermore, it can adjust with the magnitude | size and kind of layered compound. For example, it is possible not only to reduce the haze by using a layered compound that is smaller than the wavelength of visible light, but also to employ a layered compound having a refractive index close to that of the resin. Can reduce the haze.

(Film characteristics-surface roughness, coefficient of static friction)
The biaxially stretched polyamide resin film in the present invention has a very smooth surface with a surface roughness (Sa) of 0.01 to 0.1 μm, and a static friction coefficient (F / B) at a normal stress of 0.5 N / cm 2. It is preferable to satisfy 0.3 to 1.0. In general, if the surface roughness is reduced and the surface gloss is increased, the coefficient of static friction increases, and the films do not slip at all, especially under high humidity conditions, causing various troubles in the process. By biaxially stretching a polyamide resin containing an inorganic substance containing a layered compound in the invention so as to be added in an amount of 0.3 to 10% by weight at a sufficient area magnification, both surface smoothness and slipperiness can be specifically achieved. Become. This is presumably because the effect of the addition of the layered compound is exhibited at a high level, and a high elastic modulus can be maintained in a wide region from low humidity to high humidity. If the surface roughness is less than 0.01, the slipperiness may deteriorate, which is not preferable. On the other hand, when the thickness exceeds 0.1 μm, the surface gloss is not different from that of a system to which a normal lubricant is added, and does not meet the object of the present invention. When the coefficient of static friction exceeds 1.0, the slipperiness is poor, which is not preferable. The lower limit of the static friction coefficient is practically less than 0.3.

  The surface roughness can be increased by increasing the addition amount, and can be adjusted by the size and shape of the layered compound to be added. The coefficient of static friction can be adjusted by increasing the draw ratio, particularly the draw ratio in the width direction, as well as by adjusting the surface roughness.

  In addition, although it is a feature of the present invention that it is possible to achieve both surface smoothness and slipperiness without using a powdered lubricant such as spherical silica, which is generally used to improve slipping, It is also acceptable to adjust the surface roughness and slipperiness by adding a powder lubricant. When added, the average particle size of the lubricant particles is preferably 0.1 to 10 μm, more preferably 0.3 to 5 μm. The particle diameter can be measured by an electron microscope and the average value can be obtained. The addition amount is preferably 1000 ppm or less, and more preferably 700 ppm or less.

  An average particle size of 0.1 μm or less is not preferable because it is too small for the purpose of changing the surface roughness. When particles having an average particle diameter exceeding 10 μm are used or when the addition amount exceeds 1000 ppm, it is difficult to make the surface roughness 0.1 μm or less, which is not preferable.

  With reference to the preferable range described above, the surface roughness (Sa) can be appropriately adjusted so as to be 0.01 μm to 0.1 μm. As a specific adjustment method so as not to exceed 0.1 μm, the amount of addition is reduced when the particle system is large, and when the particles are aggregates of secondary particles (secondary particles). For example, particles having a large oil supply amount that easily collapses during stretching may be used. Various particles such as silica, alumina, zirconia, titania, crosslinked acrylic beads, crosslinked styrene beads, and benzoguanamine can be used as the particles.

(Film characteristics-equilibrium water absorption)
The biaxially stretched polyamide resin film in the present invention preferably has an equilibrium water absorption in the range of 3.5 to 10%. The equilibrium water absorption of a general polyamide resin biaxially stretched film is about 3%, and the biaxially stretched polyamide resin film of the present invention is preferably higher than that. Of the generally known layered compounds, montmorillonite and smectite, which are most commonly used, are generally used as thickeners for increasing the viscosity of aqueous solutions. As can be imagined from this, water is taken in between the layers, easily swells, and absorbs a large amount of water. If only these compounds are added to the resin, the montmorillonite absorbs a large amount of water. Therefore, the equilibrium water absorption of the resin composition is a large value, and the characteristics are also highly dependent on humidity. In the present invention, the layered compound is highly oriented in the plane, and the equilibrium moisture content is increased to 3.5% or more by subjecting the polyamide resin of the matrix to biaxial stretching at a high magnification and further orientational crystallization. Even with such an added amount, the humidity dependency of the characteristics can be kept low. When the equilibrium water absorption is less than 3.5%, the effect of adding the layered compound is small, and the addition amount exceeding 10% is excessive, and preferable characteristics cannot be obtained.

(Film characteristics-Elastic modulus in MD direction)
The biaxially stretched polyamide resin film of the present invention preferably has a longitudinal modulus (MD) elastic modulus in the range of 1.7 to 3.5 GPa at a relative humidity of 35%. A polyamide resin film not containing a layered compound has a high elongation and high ductility under high humidity, but conversely has a tendency that the elongation is low and brittle under low humidity. In order to increase the elastic modulus in the MD direction, it was necessary to increase not only the MD direction but also the stretching ratio in the TD direction. The biaxially stretched polyamide resin film described in the present invention can suppress the decrease in elastic modulus while maintaining the ductility under high humidity, and can improve the elastic modulus and elongation under low humidity. If the MD elastic modulus is less than 1.7 GPa, the improvement effect is small, and if it exceeds 3.5 GPa, it is difficult to balance with other characteristics, which is not preferable.

(Film characteristics-pinhole resistance)
The biaxially stretched film in the present invention is excellent in pinhole resistance, and the number of pinholes after 1000 gelboflex tests at 23 ° C. is preferably 0-30. It is mainly the stretching conditions that have an influence on the resistance to pinholes, and among them, it is preferable that the temperature during TD stretching is not particularly high. If the TD stretchability is poor, the temperature may be raised, but if the stretching temperature is raised too much above the low temperature crystallization temperature, crystallization proceeds partially without sufficient stretching, resulting in a thickness in a fine region. Unevenness and pinholes are likely to occur. Also, pinholes are likely to occur in the obtained film. Specifically, the TD stretching temperature is preferably 155 ° C. or lower. If it exceeds 155 ° C., the film becomes fragile and the pinhole resistance deteriorates, which is not preferable.

  The biaxially stretched polyamide resin film of the present invention may be subjected to corona treatment, coating treatment or flame treatment in order to improve adhesion and wettability depending on the application. In the coating process, an in-line coating method in which a film coated during film formation is stretched is one preferred embodiment. In general, the biaxially stretched polyamide resin film of the present invention is further subjected to processing such as printing, vapor deposition, and lamination depending on the application.

  The biaxially stretched polyamide resin film of the present invention includes a hydrolysis resistance improver, antioxidant, colorant (pigment, dye), antistatic agent, conductive agent, flame retardant, reinforcing agent, organic lubricant, nucleating agent, release agent. Molding agents, plasticizers, adhesion assistants, pressure-sensitive adhesives, and the like can be optionally contained.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not restrict | limited at all to these examples, unless the summary is exceeded. The measurement method used in the present invention is shown below.

(1) Haze
The sample was measured at three different locations using a haze meter (Nippon Denshoku, NDH2000) by a method according to JISK7105, and the average value was defined as haze.

(2) Glass transition temperature (Tg) measurement and low-temperature crystallization temperature (Tc) measurement An unoriented polyamide resin sheet is frozen in liquid nitrogen, decompressed and thawed, using a DSC manufactured by Seiko Denshi Co., Ltd. Measured with

(3) Addition amount of inorganic substance including layered compound (weight residue)
Using TA Instruments TGA, the weight residue was obtained after heating up to a sample amount of 0.1 g, a nitrogen stream and a temperature increase rate of 20 ° C./min to 500 ° C.

(4) Surface roughness (Sa)
Small pieces were cut from three arbitrary locations on the film, and dust and the like were carefully removed with a static elimination blower. The surface of the thermal adhesive layer was measured with a non-contact type three-dimensional shape measuring device (Micromap 557, manufactured by Micromap). The optical system used was a mirro-type two-beam interference objective lens (10 times) and a zoom lens (Bodytube, 0.5 times), and received light with a 2/3 inch CCD camera using a light source of 5600 angstroms. The measurement was performed in the WAVE mode, and a 1619 μm × 1232 μm field of view was processed as a digital image of 640 × 480 pixels. For analysis of the image, gradient removal (Detrending) was performed in the linear function mode using analysis software (Micromap 123, version 4.0). Thus, the arithmetic average surface roughness of 5 visual fields (total of 30 visual fields) for each of the three samples was measured, and the average value was defined as the surface roughness (Sa).

(5) Coefficient of static friction Measured by a coefficient of friction test method described in JIS K 7125. Ten samples were cut from five arbitrary locations on the film, and the measurement was conducted with the front and back sides of the film facing each other. The stress in the normal direction calculated from the load applied to the sliding piece was 0.5 N / cm 2, and the average value of 5 times in total was taken as the coefficient of static friction. The measurement environment was 23 ° C. and 65% RH.

(6) Gloss The glossiness (gloss) is 85 according to JIS K8741 using a gloss meter (gross meter model 1001DP (manufactured by Nippon Denshoku Industries Co., Ltd.)). The specular gloss was measured. The value was the average value of the front and back surfaces.

(3) Mechanical properties (elastic modulus)
Conforms to JIS K 7113. A sample having a width of 10 mm and a length of 100 mm in the longitudinal direction and the width direction of the film was cut out using a razor as a sample. After being left for 12 hours in an atmosphere of 23 ° C and 35% RH, the measurement was performed in an atmosphere of 23 ° C and 35% RH under the conditions of a distance between chucks of 40 mm and a pulling speed of 200 mm / min. Values were used. As a measuring device, an autograph AG5000A manufactured by Shimadzu Corporation was used.

(4) Pinhole resistance (bending fatigue resistance test)
Using a gelbo flex tester manufactured by Rigaku Corporation, the bending fatigue resistance was measured by the following method. The test was conducted using a gelbo flex tester (manufactured by Riken Corporation). First, the obtained film sample was formed into a cylindrical shape on a fixed head having a diameter of 8.89 cm (3.5 inches) and a movable head having the same diameter disposed in parallel at a distance of 17.78 cm (7 inches) from the fixed head. Attached. A shaft attached in the middle of the movable head controls the movement of the movable head. First, move the movable head 440 degrees closer to the fixed head 8.89 cm (3.5 inches), then move it closer to the fixed head 6.35 cm (2.5 inches) in a horizontal motion, Returned to the state. One cycle of this cycle was performed 1000 times at a rate of 40 times / minute at 23 ° C. and 60% RH. The number of pinholes after 1000 repetitions was measured. The number was measured by the following method. The film was placed on a filter paper (Advantech, No. 50), and the four corners were fixed with cello tape (registered trademark). Ink (pilot ink (product number INK-350-blue) diluted 5 times with pure water) was applied onto a test film and spread over one surface using a rubber roller. After wiping off unnecessary ink, the test film was removed, and the number of ink spots on the filter paper was counted.

(7) Relative viscosity 96% sulfuric acid solution 0.25 g of nylon resin was dissolved in 25 ml, and the relative viscosity was measured at 20 ° C.

(8) Observation of orientation state of layered compound in film A sample was prepared by the following method and observed using a transmission electron microscope. First, the sample film was embedded in an epoxy resin. As the epoxy resin, a mixture of Luavec 812, Luavec NMA (manufactured by Nacalai Tesque) and DMP30 (TAAB) in a weight ratio of 100: 89: 3 was used. After embedding the sample film in an epoxy resin, the sample film was left in an oven adjusted to a temperature of 60 ° C. for 16 hours to cure the epoxy resin and obtain an embedded block.

  The obtained embedding block was attached to an ultra cut N manufactured by Nissan Sangyo, and an ultrathin section was prepared. First, trimming was performed using a glass knife until a cross section of a portion desired to be observed for the film appeared on the resin surface. Next, an ultrathin section was cut out using a diamond knife (Sumitomo Electric, Sumiknife SK2045). After cutting out the ultrathin section on the mesh, carbon deposition was performed thinly. The electron microscope observation was carried out using JEM-2010 manufactured by JEOL under the condition of an acceleration voltage of 200 kV. An image obtained by electron microscopic photography of the film cross-section was recorded on an imaging plate (FDLUR-V, manufactured by Fuji Photo Film). From the images, 50 layered compounds were randomly extracted and the inclination of each was evaluated. When the variation in tilt of any layered compound falls within an angle of 20 degrees or less, it is assumed that the layers are oriented in the plane. Those that were oriented in the plane were marked with ◯, and those that were not oriented were marked with ×.

(9) Layer thickness and total number of layers in the film The film was cooled with liquid nitrogen and taken out immediately, and cut out in the width direction of the cast film or stretched film with a feather blade to obtain a cross section. This cross section was observed using an optical microscope (Olympus BX60), and a value obtained by dividing the thickness of the layer for 5 to 20 layers by the number of layers was determined as the layer thickness. The total number of layers was determined by the same method.

  When it was difficult to understand the interface of the layer by the above method, a sample was prepared by the following method and observed using a transmission electron microscope. First, the sample film was embedded in an epoxy resin. As the epoxy resin, a mixture of Luavec 812, Luavec NMA (manufactured by Nacalai Tesque) and DMP30 (TAAB) in a weight ratio of 100: 89: 3 was used. After embedding the sample film in an epoxy resin, the sample film was left in an oven adjusted to a temperature of 60 ° C. for 16 hours to cure the epoxy resin and obtain an embedded block. The obtained embedding block was attached to an ultra cut N manufactured by Nissan Sangyo, and an ultrathin section was prepared. First, trimming was performed using a glass knife until a cross section of a portion desired to be observed for the film appeared on the resin surface. Next, an ultrathin section was cut out using a diamond knife (Sumitomo Electric, Sumiknife SK2045). After cutting out the ultrathin section on the mesh, carbon deposition was performed thinly.

  The electron microscope observation was carried out using JEM-2010 manufactured by JEOL under the condition of an acceleration voltage of 200 kV. An image obtained by electron microscopic photography of the film cross-section was recorded on an imaging plate (FDLUR-V, manufactured by Fuji Photo Film). From the image, the thickness of the layer having the maximum thickness was measured from the distance between the interfaces of each layer.

Hereinafter, Examples 1, 2, and 5-7 are read as Reference Examples 1, 2, and 5-7.
Example 1
Nylon 6 resin pellets (T-800 manufactured by Toyobo Co., Ltd .: relative viscosity RV = 2.5, no lubricant) and montmorillonite uniformly dispersed as a layered compound (Nanopolymer Composite Corp. manufactured) NF3040, amount of layered compound added: 4% (inorganic content 2.6%)
Each was vacuum dried at 100 ° C. overnight and then blended at a weight ratio of 1/1. The blended pellets were then fed into two extruders. Melting at 270 ° C, laminating the same kind of resin using a 16-element static mixer at 275 ° C, and 270 in sheet form on a cooling roll adjusted to 20 ° C
A multilayer unstretched sheet was produced by extruding from a T-die heated to ° C and solidifying by cooling.
The ratio of the discharge amount of the two extruders was 1: 1. The thickness of the unstretched sheet was 180 μm, and the thickness of each layer at the center in the width direction was about 1 μm. The sheet had a Tg of 35 ° C. and a melting point of 225 ° C. This sheet is first preheated at a temperature of 65 ° C., then MD stretched at a stretching temperature of 65 ° C. at a deformation rate of 16000% / min. 2.5 times, and this sheet is continuously led to a tenter, and the remaining heat zone 65 ℃
, TD-stretched 3.8 times at 135 ° C, heat-fixed at 210 and subjected to 5% transverse relaxation treatment, cooled, cut and removed both edges, and 12μm thick biaxially stretched polyamide resin film Got.
The film had a width of 40 cm and a length of 1000 m and was wound around a paper tube. Table 1 shows the film physical properties at this time.

(Examples 2-5, Example 7, Comparative Examples 1-2, Comparative Examples 4-6)
Samples were prepared under the conditions described in Table 1. Table 1 shows the film characteristics and the like of the examples, and Table 2 shows the film characteristics and the like of the comparative example.

  In Example 3 and Comparative Example 1, a single layer was used without using a static mixer. In Examples 4 and 5, TD stretching was performed after MD two-stage stretching.

(Example 6)
Nylon 6 resin pellets in which montmorillonite is uniformly dispersed as a layered compound (NF3040 from Nanopolymer Composite Corp., addition amount of layered compound: 4% (inorganic content 2.6%), organically treated montmorillonite powder (Cloisite 30B, Southern Clay Products) Were dried in a vacuum overnight at 100 ° C., then dry blended so that the amount of layered inorganic compound added was 8%, and then charged into a twin-screw extruder and melt-mixed at 275 ° C. The resin pellets were again dried for 24 hours in a vacuum dryer at 100 ° C. The resin was fed to the extruder, melted at 275 ° C., and the same kind of resin was used using a 275 ° C. 16 element static mixer. Was laminated on a cooling roll adjusted to 20 ° C. and extruded from a T-die heated to 270 ° C., and cooled and solidified to produce a multilayer unstretched sheet having a thickness of 180 μm and a center in the width direction. The thickness of each layer was about 1 μm, and the Tg of this sheet was 35 ° C. and the melting point was 225 ° C. The sheet was first preheated at a temperature of 45 ° C., and then a roll having a surface temperature of 85 ° C. Then, MD stretching was performed 3.2 times at a deformation rate of 4500% / min, and this sheet was continuously led to a tenter, TD-stretched 3.8 times at a preheating zone of 110 ° C and a stretching zone of 130 ° C, and heat-fixed at 210 ° C. The film was cooled after 5% lateral relaxation treatment, and both edges were cut and removed to obtain a biaxially stretched polyamide resin film having a thickness of 15 μm.

(Comparative Example 3)
Nylon 6 resin pellets (T-800, manufactured by Toyobo Co., Ltd .: relative viscosity RV = 2.5, without lubricant), silica particles as a lubricant (Fuji Silysia Chemical Co., Ltd., Silicia 310) at 100 ° C. After vacuum drying overnight, the mixture was mixed by an extruder at 270 ° C., and melt mixed at 275 so that the lubricant concentration was 1000 ppm. The obtained resin pellets were again dried in a vacuum dryer at 100 ° C. for 24 hours. This resin was supplied to an extruder, melted at 275 ° C, the same kind of resin was laminated using a 16-element static mixer at 275 ° C, and heated to 270 ° C in a sheet form on a cooling roll adjusted to 20 ° C. A multilayer unstretched sheet was produced by extruding from a die and cooling and solidifying. The thickness of the unstretched sheet was 180 μm, and the thickness of each layer at the center in the width direction was about 1 μm. The sheet had a Tg of 35 ° C. and a melting point of 225 ° C. This sheet is first pre-heated at a temperature of 45 ° C, then MD-stretched 3.2 times at a deformation rate of 16000% / min with a roll with a surface temperature of 60 ° C, and this sheet is continuously led to a tenter to keep the remaining heat. TD-stretched 3.8 times in zone 110 ° C and stretching zone 130 ° C, heat-fixed at 210 ° C and 5% transverse relaxation treatment, then cooled, both edges cut and removed, biaxial 15μm thick A stretched polyamide resin film was obtained. Table 2 shows the film physical properties at this time.

  Since the slipperiness of conventional nylon films changes with humidity, when slipperiness under high humidity is required, the surface roughness is roughened to make it slippery, but inorganic layered compounds are used. In conventional films, the change in slipperiness due to humidity is small, and even if the surface roughness is small, sufficient slipperiness is exhibited, so that conflicting properties such as gloss can be achieved.

Claims (4)

An inorganic substance containing a layered compound is added in an amount of 0.3 to 10% by weight, and the polyamide resin used in the biaxially stretched polyamide resin film is a kind of resin selected from nylon 6, nylon 66, and metaxylylenediamine-based nylon. The compound is oriented in-plane, the haze is 1.0-20%, the elastic modulus in the longitudinal direction at a relative humidity of 35% RH is 1.7-3.5 GPa, the surface roughness (Sa) is 0.01-0.1 μm, the normal stress When the coefficient of static friction (F / B) at 0.5 N / cm ² is 0.3 to 1.0 and the refractive index of the central portion in the width direction of the film is Ny, Ny (A) which is Ny of the sheet before longitudinal stretching A method for producing a biaxially stretched polyamide resin film in which the difference Ny (A) −Ny (B) from Ny (B) of the sheet after longitudinal stretching is 0.001 or more, and a speed of 2000% / min or less The manufacturing method of the biaxially stretched polyamide resin film characterized by including the process stretched | stretched longitudinally. 2. The method for producing a biaxially stretched polyamide resin film according to claim 1, wherein the number of pinholes after 1000 gelboflex tests at 23 ° C. is 0 to 30. 3. The method for producing a biaxially stretched polyamide resin film according to claim 1 or 2, wherein the biaxially stretched polyamide resin film is stretched transversely at a transverse stretching temperature of 50 to 155 ° C. The method for producing a biaxially stretched polyamide resin film according to any one of claims 1 to 3 , wherein the stretching in the longitudinal direction is a single step or a two-step stretch.